Steam currently lists the supported OS as Windows XP SP2+, Vista, and 7 (same as The Journey Down 1 and 2)

GOG currently lists the supported OS as Windows 7/8/10

flotsam played using Windows 10

Unless we hear differently from the developer, we're assuming the game is compatible with all these OS(every version of Windows from XP SP2 through Windows 10)If this turns out not to be the case, the specs listed in the review will be edited